A mutant of Salmonella typhimurium with an abnormal septation pattern associated with an inhibition of RNA synthesis

Abstract

A mutant strain of S. typhimurium that is disturbed in the regulation of cell division and macromolecular synthesis is described. The life cycle of the mutant can be divided into two discrete stages. When growing in rich medium at a low cell density, cell division is inhibited and the cells filament at the same time as the relative amount of RNA shows a continuous increase. However, at a certain stage, RNA synthesis stops and the filaments start to septate resulting in chain‐formation. These chains can thereafter segregate into individal cells of unit cell length. The accumulation of RNA is rather due to a regulatory defect in the synthesis of the stable RNA species than to an unusual stability of messenger RNA (mRNA)as the half life of mRNA was estimated to 2.3 minutes during the period of RNA accumulation. Latter inhibition of RNA synthesis affects only stable species of RNA. The ppGpp pools of the strain did not fluctuate during growth, showing that inhibition of RNA synthesis is not correlated to changes in the level of ppGpp. Different treatments that reduce the level of transcription such as sublethal concentrations of rifampicin, a shift‐down or high concentrations of nalidixic acid, all induced cell division of filamentous cells, suggesting that there exists an intimate relationship between macromolecular synthesis and cell division. The behaviour of this mutant fits best with the proposed hypothesis that the biomass to volume ratio is of importance in the regulation of cell division in bacteria.